Gas turbine engines include one or more compressors for pressurizing a working medium fluid, typically ambient air, which flows through a longitudinally extending compressor flow path. Under some operating conditions, it is desirable to temporarily moderate the pressure at the discharge end of the compressor to prevent or recover from compressor stall or other aerodynamic instabilities. Pressure moderation is usually effected by opening a compressor bleed valve that diverts a portion of the pressurized fluid from the discharge end of the compressor flow path into a lower pressure region.
An exemplary compressor bleed valve system includes a moveable full hoop valve ring with a pair of ring seal members radially aligned with the bleed duct case seal seats. The compressor bleed valve includes a ring having a pair of resilient seal members adhesively bonded or clamped into respective channels on longitudinally facing surfaces of the ring. A series of circumferentially distributed passages extend through the bleed duct case to join the compressor flow path to a surrounding annular chamber. A set of pins extends radially from the valve ring, and each pin includes a roller that engages a carved slot on the orifice ring. A bell crank for operating the valve ring is mounted on a bell crank support bracket by a bell crank pivot. Input and output arrays of the bell crank are connected respectively to an actuator and to the valve ring.
In operation, the actuator rotates the bell crank about the bell crank pivot so that the bell crank, in turn, drives the valve ring in a spiral motion, positioning the sleeve to cover or uncover the passages. The rollers help guide the valve ring in its spiral path. As the valve ring approaches its fully closed position, the seal members contact the seal seats, compressing them in the longitudinal direction to affect a fluid tight seal.